RM  LIBRARY 


ci«.AA^Ji   JEAsK 


A  FOSSIL  FLOWER 


Published  by 

FIELD  MUSEUM  OF  NATURAL  HISTORY 

CHICAGO 

1924 


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Field  Museum  of  Natural  History 

DEPARTMENT  OF  BOTANY 
Chicago,  1924 

Leaflet  Number  5 

A  FOSSIL  FLOWER 

One  of  the  last  official  signatures  of  President 
Harding  was  affixed  to  an  act  establishing  the  Cycad 
National  Monument,  the  story  of  which  forms  an 
interesting  chapter  in  the  history  of  recent  botanical 
science. 

The  tract  of  land  in  the  southern  Black  Hills  of 
Dakota  thus  designated  and  now  set  apart  "for  all 
time"  is  neither  especially  distinguished  for  grandeur 
of  landscape,  magnificence  of  present  vegetation,  nor 
for  other  openly  striking  features.  Nevertheless  it 
is  a  place  justly  famous  among  botanists  the  world 
over. 

The  locality  had  attracted  attention  nearly  a  cen- 
tury ago.  In  the  course  of  the  adventures  related  by 
Edgar  Allan  Poe  in  The  Thousand-and-second  Tale 
of  Scheherazade,  Sinbad  and  his  companion  encoun- 
tered an  island  "where  the  forests  were  of  solid  stone, 
and  so  hard  that  they  shivered  to  pieces  the  finest- 
tempered  axes.  .  .  ."  In  a  footnote  to  this  tale  there  is 
mentioned  by  way  of  corroboration  "the  discovery 
of  a  completely  petrified  forest  near  the  head  waters 
of  the  Cheyenne,  or  Chienne  River,  which  has  its 
source  in  the  Black  Hills  of  the  Rocky  chain." 

That  an  unparalleled  record  of  extinct  life  of  the 
Reptilian  Age  lies  imbedded  in  the  rocks  of  this  for- 
mation was  scarcely  suspected  until  about  thirty  years 
ago.    It  was  not  until  then  that  the  locality  received 

[41] 


2  Field  Museum  of  Natural  History 

scientific  attention1  and  some  of  its  fossil  tree 
trunks  were  described.  They  had  been  looked  upon 
mainly  as  remains  of  fairly  well-known  cone-bearing 
plants,  though  among  them  had  been  noted  stems, 
suggestive  of  both  tree-ferns  and  so-called  sago 
palms.  These  were  determined  to  be  fossil  cycads 
of  a  type  already  known,  especially  in  Europe,  but 
more  perfectly  preserved  than  any  hitherto  seen.  The 
fame  of  the  locality,  however,  rests  chiefly  on  the 
subsequent  and  surprising  discovery  that  many  of 
these  fossil  trunks  bore  actual  flowers.  These  were 
brought  to  light  by  Professor  Wieland  of  Yale2. 
Indicating  that  real  floral  structures  had  originated 
much  earlier  than  had  heretofore  been  supposed, 
these  ancient  and  primitive  flowers  differ  in  many 
respects  from  those  of  the  later  true  flowering  plants 
and  have  proved  to  be  botanically  of  extraordinary 
interest. 

The  plants  which  bore  these  flowers  flourished 
millions  of  years  ago,3  when  egg-laying  monsters 
were  still  extant.       The  common  name  "Cycadeoid" 

1.  Professor  Thos.  H.  Macbride  of  Iowa  published  the 
first  description  of  a  Black  Hills  cycad  in  1893.  Professor 
O.  C.  Marsh  of  Yale  soon  afterwards  made  a  very  extensive 
collection  of  the  trunks.  Professor  Lester  F.  Ward  made 
several  reconnaissances  of  the  region  and  described  numerous 
species   of   these  fossils. 

2.  Less  extensive  material  of  similar  kind  in  less  per- 
fect stages  of  petrification  had  also  been  studied  by  European 
botanists,  but  without  finality  of  results,  when  Professor  G.  R. 
Wieland  in  1898  began  his  searching  investigation  of  the 
Black  Hills  material,  both  in  the  field  and  laboratory.  He 
was  soon  able  to  report  surprising  discoveries,  and  to  make 
some  of  the  most  critical  and  important  additions  to  paleo- 
botany, or  the  knowledge  of  ancient  plants,  in  perhaps  a  gen- 
eration. 

3.  The  age  of  the  formation  in  which  they  were  found 
has  been  variously  estimated.  On  the  basis  of  the  disintegra- 
tion rate  of  radio-active  minerals  it  exceeds  a  hundred 
million  years. 

The  earliest  known  cycadeoid  remains  date  from  the 
Triassic,  the  latest  from  the  Cretaceous.  Their  distribution  in 
time  thus  covers  the  entire  Mesozoic.  The  foliage  type  is 
even  older. 

[42] 


A  Fossil  Flower 


Fig.  2. 

A  LIVING  CYCAD. 

(Dioon  edule). 

The  living  cycads  constitute  a  small  and  dwindling  group,  confined^  almost 
exclusively  to  the  tropics.  The  "armour"  formed  by  old  leaf-bases  remaining  on 
the  trunk,  is  a  characteristic  feature  of  the  cycads,  plainly  to  be  seen  in  this  fine 
photograph  of  a  Mexican  plant. 

Photograph  by  Professor  C.  J.  Chamberlain. 


[43] 


4  Field  Museum  of  Natural  History 

meaning  cycad-like,  is  from  the  generic  name  Cycade- 
oidea  used  about  a  century  ago  by  the  celebrated  Dean 
Buckland4  for  specimens  of  their  kind  from  the  Isle 
of  Portland  on  the  south  coast  of  England.  The 
Cycadeoids  are  related  to  the  living  cycads  which  in- 
clude some  so-called  Sago  Palms,  and  resemble  them 
in  stem  structure  and  foliage,  yet  the  presence  of 
flowers  places  them  in  a  separate  group.  Being  en- 
tirely extinct,  they  are  commonly  and  not  incorrectly 
spoken  of  as  "fossil  cycads",  as  by  using  this  term 
in  a  wide  sense  the  cumbersome  technical  name  is 
avoided.  During  the  Reptilian  or  Mesozoic  Age,  the 
medieval  era  in  the  history  of  life  on  earth,  the  fossil 
cycads  probably  constituted  at  least  a  third  of  the 
vegetation.  This  age  is  therefore  also  known  as  the 
Age  of  Cycads.  On  the  basis  of  its  chief  vegetation 
the  succeeding  Age  of  Mammals,  which  includes  the 
present  day,  is  characterized  as  the  Age  of  the  Flower- 
ing Plants.  However,  it  was  shown  by  Professor 
Wieland's  investigations  that  the  dominant  types  of 
the  vegetation  even  in  the  mid-geologic  era,  had 
reached  an  actual  flowering  stage. 

Some  plants  of  the  Cycadeoid  group  were  small- 
leaved  and  branched,  and  in  general  appearance  must 
have  been  comparable  to  the  simpler  forms  of  modern 
trees.  They  were  no  doubt  the  very  numerous  for- 
est members  of  their  kind.  The  great  mass  of  the 
petrified  forms  which  have  been  discovered  were 
thick-stemmed,  globular  to  low  columnar  plants,  most- 
ly unbranched,  though  some  are  forked  after  the 
manner  of  cacti.  They  grew  probably  on  the  edge 
of  deserts. 


4.  English  clergyman  and  geologist,  author  of  the  Bridge- 
water  Treatise  on  Geology,  Dean  of  Westminster.  Buckland 
had  advised  with  Robert  Brown,  the  botanist,  who  suggested  a 
family  name,  the  Cycadeoidese.  The  term  Bennettiteae  is  pre- 
ferred by  some  botanists. 

[44] 


A  Fossil  Flower  5 

Trunks  of  the  thick-stemmed  kind  have  been 
found  in  a  few  localities  in  Europe,  in  Afghanistan 
and  in  India.  One  such  petrified  stem,  now  in  an 
Italian  museum,  was  found  in  an  old  Etruscan  necrop- 
olis or  burial  place  near  Bologna,  where  it  had  been 


•r—  ."r  ^L  ^* 


Fig.  3. 

A  FOSSIL  CYCAD  TRUNK. 

(Cycadeoidea  dacotensis). 

Numerous  large  fructifications  enclosed  by  their  bracts  are  conspicuous 

among  the  pits  which  mark  the  ends  of  the  leaf-bases.    This  magnificent  silic- 

ified  trunk  was  the  first  specimen  described  from  the  Black  Hills. 

Courtesy  of  Professor  T.  H.  Macbride. 

placed  on  a  tomb  by  the  Etruscans  who  obtained  it 
from  the  near-by  Apennine  hills  over  four  thousand 
years  ago.  About  a  thousand  of  these  trunks  have 
been  discovered  in  the  United  States.    The  great  mass 

[46] 


6  Field  Museum  of  Natural  History 

of  them  comes  from  the  Black  Hills  of  Dakota,  the 
most  numerous  and  important  specimens  being  ob- 
tained from  within  the  actual  limits  of  the  Cycad 
National  Monument.  Others  have  been  found  in  Wy- 
oming, also  in  Maryland  between  the  cities  of  Wash- 
ington and  Baltimore,  and  isolated  stems  have  been 
collected  in  Texas,  Colorado  and  California.  They 
were  early  recognized  as  fossils,  although  not  always 
suspected  to  be  plants.  Their  appearance  is  unusual 
and  has  attracted  attention  wherever  they  were  found. 
The  miners  in  the  Potomac  region  kept  them  as  curi- 
osities in  their  homes,  regarding  them  as  fossil  bee- 
hives and  wasp-nests.  The  workmen  in  the  quarries  of 
Portland,  England,  where  they  are  encountered,  long 
ago  dubbed  them  "crows-nests."  As  in  the  cycads,  the 
leaf  bases  in  these  plants  remained  after  the  foliage 
wilted  down  and  now  make  up  the  outer  layer,  or 
"armour",  of  the  trunks,  at  the  surface  of  which  the 
spirally  disposed  ends  usually  appear  as  depressions  or 
pits.  On  this  account  the  trunks  were  described  by 
some  early  writers  as  petrified  "masses  of  coral-cups" 
or  as  "clusters  of  barnacles." 

Professor  Wieland  found  his  fossil  flowers  secure- 
ly encased  in  this  outer  layer  of  the  trunks.  They 
were  present  mostly  in  the  form  of  unexpanded  buds 
but  in  many  instances  fruits  had  begun  to  mature. 
No  actually  open  flowers  have  ever  been  found.  Nat- 
urally any  that  were  present  when  the  chain  of  events 
leading  to  fossilization  began,  wilted  and  must  have 
been  quickly  destroyed,  as  may  be  easily  surmised 
after  a  glance  at  the  delicate  expanded  structure.  It 
was  the  fortunate  preservation  of  the  well-protected 
buds  in  a  petrified  state  that  made  possible  the  inves- 
tigation of  their  nature.  It  is  likely  that  these  ex- 
tinct plants,  like  the  century  plant  or  the  Talipot  palm, 
flowered  only  once  after  a  prolonged  vegetative 
period,  and  then  died  down.    The  flowering  must  have 

[46] 


A  Fossil  Flower 


Figr.  4. 

A  FOSSIL  CYCAD  IN  FLOWER. 

This  figure  represents  the  conception  of  the  famous  paleobotanist,  Nalthorst. 
The  original  painting  is  in  the  National  Museum,  Stockholm. 

Courtesy  of  Professor  G.  R.  Wieland. 


[47] 


s 


Field  Museum  of  Natural  History 


been  profuse,  for  some  of  the  trunks  preserved  in  the 
critical  stage  show  upwards  of  five  hundred  buds. 
The  position  of  the  flowers  on  the  old  part  of  the 
trunk  is  unusual,  but  is  not  entirely  unique,  for  a 
somewhat  similar  flowering  habit  is  to  be  seen  among 
some  of  the  tropical  forest  trees. 


Fig.  5. 

A  FOSSIL  CYCAD  FLOWER. 

(Cycadeoidea  ingens). 

Photograph  of  the  model  in  the  Field  Museum  of  Natural  History. 

By  the  use  of  a  tubular  drill,  Professor  Wieland 
removed  the  buds  and  fruits  from  the  petrified  trunks. 
The  cores  thus  secured  were  sliced  and  polished,  so 
that  the  structures  enclosed  became  plainly  exposed 

[48] 


A  Fossil  Flower 


9 


to  view.  The  preservation  is  often  so  perfect  that 
microscopic  details,  such  as  pollen  grains,  may  be  as 
clearly  observed  as  in  living  plants,  and  the  study  of 
an  abundance  of  sectioned  material  has  resulted  in  a 
clear  comprehension  of  the  structure. 

The  most  striking  feature  of  one  of  these  flowers 


Fig.  6. 

A  FOSSIL  CYCAD  FLOWER. 

(Cycadeoidea  ingens). 

Photograph  of  the  model  in  the  Field  Museum  of  Natural  History.    Same  as 
figr.  5,  seen  from  above. 

is  its  branched  stamens,  which  number  a  dozen  or 
more,  resembling  the  fertile  fronds  of  certain  ferns. 
The  stamens  are  laterally  united  at  the  base  and 
fused  to  a  corolla-like   "disk."     The   disk  with   the 

[49] 


10  Field  Museum  of  Natural  History 

stamens  was  thrown  off  as  soon  as  the  function  of  the 
latter  was  fulfilled.  Similar  but  simpler  disks  had 
previously  puzzled  geologists  who  found  them  as 
detached  specimens  in  various  places.  The  center  of 
the  flower  is  occupied  by  a  seed-producing  cone,  as  is 
the  case  in  the  magnolias,  especially  in  the  tulip 
tree.  In  its  minute  structure  the  fossil  cone  is, 
however,  quite  different  from  that  of  these  flowering 
trees,  for  the  seeds  are  still  naked  instead  of  enclosed 
as  in  the  present  true  flowering  plants.  Below  the 
disks  are  numerous  bracts,  or  "sepals",  as  they  would 
be  called  in  a  modern  flower.  These  constituted  an 
outer  protecting  envelope  which  remained  to  surround 
the  fruit  as  it  matured.  All  the  usual  parts  of  a  flow- 
er are  seen  to  be  present  and  disposed  in  the  usual 
sequence.  This  fossil  flower  is  thus  unmistakably  a 
flower  according  to  all  definitions — "the  flower  of 
Linnaeus,  of  Goethe,  and  of  Payer",  as  their  discov- 
erer states. 

It  is  quite  natural  to  ask,  what  may  be  the  con- 
nection between  these  ancient  flowers  and  those  of 
the  modern  flowering  plants. 

The  origin  of  the  flowering  plants  proper  is  ob- 
scure. Their  first  appearance  as  leaf -impressions  in  the 
rocks  dates  from  the  latter  half  of  the  Age  of  Cycads. 
From  the  numbers  and  the  considerable  variety  of 
their  earliest  traces,  it  is  certain  that  they  were  then 
already  far  advanced.  A  long  evolutionary  history, 
which  remains  unknown,  unquestionably  lies  behind 
their  sudden  rise  to  visibility.  It  was  this  late  and 
apparently  abrupt  appearance  of  the  flowering  plants 
that  was  referred  to  by  Darwin  as  an  "abominable 
mystery." 

In  the  absence  of  fossil  clues,  the  origin  of  the 
now  dominant  flowering  plants  is  an  unsolved  prob- 
lem in  spite  of  the  intensive  study  of  living  plants  that 
has  been  carried  on  for  generations.     Botanists  are 

[50] 


A  Fossil  Flower 


11 


not  agreed  as  to  which  of  the  many  kinds  of  flower- 
ing plants  may  be  assumed  to  be  most  primitive  and 
to  represent  the  nearest  approach  to  an  ancestral  type. 
Indeed,  botanical  classification  of  the  flowering  plants 
is  expressive  of  the  uncertainty  which  prevails. 

Such  being  roughly  the  state  of  our  knowledge 
— or  ignorance — of  the  origin  and  primitive  state  of 
the  true  flowering  plants,  the  question  inevitably 
arises  whether  the  ancient  flowers  of  the  fossil  cycads 


Fijr.  7. 

A  schematic  flower  of  a  hypothetical  stock  ancestral  to 
cycads  and  flowering:  plants. 

From  Arber  and  Parkin. 

may  not  represent  the  ancestral  type.  The  particular 
one  described  and  figured  here  is  considered  much  too 
specialized  to  be  the  ancestor  of  anything.  It  must 
rather  be  considered,  with  the  plants  to  which  it  be- 
longed, to  have  been  an  end-product,  or  a  final  devel- 
opment in  a  vanishing  line.  However,  some  flowers 
of  simpler  fossil  cycads  of  a  less  peculiar  habit  of 
growth  have  also  been  discovered.  The  degree  of  rela- 
tionship of  the  fossil  cycads  to  the  stock  from  which 

[51] 


12 


Field  Museum  of  Natural  History 


the  flowering  plants  sprang  has  not  been  defined,  but 
the  consensus  of  opinion  seems  to  be  that  the  two 
lines  are  at  best  only  distantly  connected.  The  near- 
est relationship  that  appears  to  be  possible  is  a  con- 
nection by  common  descent  from  a  still  older  group. 
Nevertheless  it  is  difficult  to  escape  the  growing 
conviction  that  these  fossil  flowers  shed  light  on  the 
early  floral  structure  of  the  true  flowering  plants.  It 
is  tempting  to  assume,  at  least  by  the  way  of  hypothe- 


Fig.  8. 

A  purely  hypothetical  primitive  flower  of  the  true 
flowering  plants. 

From  Arber  and  Parkin. 

sis,  that  the  ancestors  of  these  bore  flowers  organized 
on  a  similar  plan.5  The  well-known  English  author- 
ity, Scott,  thus  says  of  the  cycadeoid  flowers,  that  they 
"for  the  first  time  brought  the  origin  of  the  flowering 
plants  within  the  range  of  scientific  discussion." 

The  alterations  which  would  be  required  to  trans- 
form the  cycadeoid  flower  into  that  of  the  later  flow- 
ering plant  can  easily  be  specified.     Restorations  of 


5.  "The  cycadeoid  flowers  show  the  possibilities  and 
trends  of  variation  and  even  the  lines  along  which  variation 
could   primarily   occur."      Wieland. 

[52] 


A  Fossil  Flower 


13 


hypothetical  ancestral  flowers  have  been  attempted 
by  Wieland  and  others  on  this  basis  and  visualized  by 
the  English  botanists  Arber  and  Parkin  as  reproduced 
in  Figures  7  and  8.  If  their  conception  is  accepted 
as  correct  in  principle,  the  so-called  "strobilus  theory" 
of  the  flower  becomes  the  only  tenable  one.  Accord- 
ing to  this  the  various  parts  of  the  primitive  flower 
were  disposed  in  the  form  of  a  cone,  terminal  on  the 
flowering  axis.    Its  seed-bearing  members  were  placed 


Fig.  9. 
A  TULIP-TREE  FLOWER. 
The  carpels  are  seen  to  form  a  strobilus  or  cone.     In  the  magnolia  the  stamens 
are  more  numerous  and  arranged  in  a  more  definitely  spiral  manner. 
From  Sargent. 

at  the  tip,  followed  in  order  by  stamens  and  below 
these  by  the  sterile  members  which  are  generally 
known  as  petals  and  sepals.  The  parts  are  assumed 
to  be  indefinite  in  number,  and  spirally  arranged.  The 
most  primitive  flowers,  according  to  this  theory,  are 
those  of  the  magnolia  order,  with  the  tulip  tree  flower 
approaching  perhaps  more  closely  than  any  other  to 
the  ideal  type.*  This  well-known  theory  has  long  been 
entertained  by  many  botanists  who  now  find  support 


Wieland,  1901. 


[53] 


14 


Field  Museum  of  Natural  History 


for  their  views  in  these  fossil  flowers.  Others,  more 
skeptical,  refuse  to  attach  any  special  significance  to 
the  older  cycad  floral  type  taken  as  a  hypothetical 
"missing  link." 


Fig.  10. 

Stages  in  the  reduction  of  stamens  from  the  frond-like  condition 
in  fossil  cycad  flowers  (1.  Cycadeoidea,  2.  WiUiamsonia),  through  a 
hypothetical  intermediate  stage  (3),  to  the  condition  in  a  flowering 
plant  such  as  the  morning-glory  (4). 

From  Wieland. 


The  presence  of  the  bell-shaped  disk  uniting  the 
stamens  has  led  to  some  speculation,  particularly 
since  it  has  also  been  found  in  another  cycadeoid  with 

[54] 


A  Fossil  Flower  15 

unbranched  stamens.  Professor  Wieland6  points  out, 
that  with  the  stamens  reduced  to  simplest  form,  this 
disk  or  "campanula"  would  make  a  perfect  corolla 
of  the  morning-glory  type.  The  possibility  is  sug- 
gested that  this  feature  may  have  been  present  also 
among  some  members  of  the  primitive  flowering  stock 
and  that  the  origin  of  the  corolla  of  many  flowers 
of  the  tubular  type  may  be  far  more  ancient  than  is 
is  ordinarily  supposed.  Such  are  a  few  of  the  botani- 
cal questions  which  are  raised. 

Entirely  apart  from  their  theoretical  importance 
and  possible  bearing  on  the  evolutionary  history  of  the 
flowering  plants,  these  early  flowers  are  in  them- 
selves objects  of  great  interest.  Considering  the  per- 
ishable nature  of  flowers  and  the  delicate  character 
of  many  of  their  parts,  the  fact  of  their  perfect  pres- 
ervation through  millions  of  years  seems  remarkable. 
To  bring  to  light  and  to  restore  with  confidence  ex- 
tinct flowers  which  bloomed  at  the  time  when  the 
earliest  birds  were  learning  to  fly  is  no  small  achieve- 
ment. The  published  results  of  Professor  Wieland's 
investigations  fill  two  large  illustrated  volumes  issued 
by  the  Carnegie  Institution  of  Washington,  and  a 
third,  of  equal  interest,  published  by  the  Geological 
Institute  of  Mexico. 

Realizing  the  desirability  of  conserving  the  site 
that  yielded  these  fossil  trunks,  Professor  Wieland 
had  the  foresight  to  secure  its  immediate  protection  by 
filing  a  homestead  claim  to  the  tract  of  320  acres.  It 
is  due  to  his  initiative  that  this  tract,  which  he  later 
released  for  the  purpose,  is  now  preserved  as  a  Nat- 
ional Monument  of  unique  botanical  interest. 

A  reconstruction  or  model  of  this  fossil  flower 
as  restored  by  Professor  Wieland  has  been  produced 
with  his  cooperation  in  the  Stanley  Field  Laboratories 


6.    Wieland,  G.  R.,  Botanical  Gazette,  Dec.  1909. 

[55] 


16  Field  Museum  of  Natural  History 

of  the  Field  Museum  of  Natural  History.  It  will  be 
placed  near  the  modern  cycads  in  the  hall  devoted  in 
this  Museum  to  a  synopsis  of  the  plant-life  of  the 
world. 

B.  E.  Dahlgren. 


Fossil  Cycad  trunks  and  leaves  are  found  in  the  ex- 
hibits of  the  Department  of  Geology  in  the  west  hall  (Hall 
38)  on  the  second  floor. 

In  the  Department  of  Botany  the  Cycads  are  to  be  seen 
in  the  Hall  of  Plant  Life,  in  the  east  hall  (Hall  29),  also  on 
the  second  floor. 


[56] 


